Many diseases of the central nervous system are influenced by the adrenergic, the dopaminergic and the serotoninergic neurotransmitter systems. Serotonin has been implicated in numerous diseases and conditions, which originate from central nervous system. Such CNS diseases and conditions are linked to sleeping, eating, perceiving pain, controlling body temperature, controlling blood pressure, depression, anxiety, schizophrenia and other bodily states. (References: Fuller, R. W., Drugs Acting on Serotoninergic Neuronal Systems, in “Biology of Serotoninergic Transmission”, ed. by Osborne N. N., J Wiley & Sons Inc. (1982), 221-247; Boullin D. J., et. al., in “Serotonin in Mental Abnormalities”, International Association for The Scientific Study of Mental Deficiency, Wiley, Checester, 1978, pp. 1-340; Barchas J. et. al., in “Serotonin and Behavior”, Academic Press, NY (1973)). Serotonin also plays an important role in the peripheral systems, such as the gastrointestinal system, where it has been found to mediate a variety of contractile, secretory and electrophysiologic effects.
Due to the broad distribution of serotonin within the body, there is a lot of interest and use, in the drugs that affect serotoninergic systems. Particularly, preferred are those compounds, which have receptor-specific agonism and/or antagonism for the treatment of a wide range of disorders, such as anxiety, depression, hypertension, migraine, obesity, compulsive disorders, schizophrenia, autism, certain neurodegenerative disorders like Alzheimer, Parkinson, Huntington's chorea and chemotherapy-induced vomiting (References: Gershon M. D. et. al., 5-Hydroxytryptamine and enteric neurons, in the book: The Peripheral Actions of 5-Hydroxytryptamine, edited by J. R. Fozard. New York: Oxford, 1989, p. 247-273; Saxena P. R., et al., Journal of Cardiovascular Pharmacology (1990), supplement 15, p. 17-34).
The major classes of serotonin receptors (5-HT1-7) contain fourteen to eighteen separate receptors that have been formally classified (References: Glennon et al, Neuroscience and Behavioral Reviews (1990), 14, 35; and Hoyer D. et al, Pharmacol. Rev. (1994), 46, 157-203). Recently discovered information regarding sub-type identity, distribution, structure and function suggests that it is possible to identify novel, sub-type specific-agents having improved therapeutic profiles with lesser side effects. The 5-HT6 receptor was identified in 1993 (References: Monsma et al, Mol. Pharmacol. (1993), 43, 320-327; and Ruat M. et al, Biochem. Biophys. Res. Com. (1993), 193, 269-276). Several antidepressants and atypical antipsychotics bind to the 5-HT6 receptor with high affinity and this binding may be a factor in their profile of activities (References: Roth et al, J. Pharm. Exp. Therapeut. (1994), 268, 1403-1410; Sleight et al, Exp. Opin. Ther. Patents (1998), 8, 1217-1224; Bourson et al, Brit. J. Pharmacol. (1998), 125, 1562-1566; Boess et al, Mol. Pharmacol., 1998, 54, 577-583; Sleight et al, Brit. J. Pharmacol. (1998), 124, 556-562). In addition, 5-HT6 receptor has been linked to generalized stress and anxiety states (Reference: Yoshioka et al, Life Sciences (1998), 17/18, 1473-1477). Together these studies and observations suggest that the compound, which antagonizes 5-HT6 receptors, will be useful in treating various disorders of the central nervous system. It has also been reported that antagonism of 5-HT6 receptor could promote neuronal growth within the central nervous system of a mammal (WO 03/066056 A1).
There is very strong evidence that Melatonin is important for the regulation of a variety of neural and endocrine functions, especially those that exhibit circadian and circannual rhythmicity. Great interest therefore lies in the possibility of making available to the clinician melatonin analogues that are metabolically more stable and have an agonist or antagonist character and of which the therapeutic effect may be expected to be superior to that of the hormone itself. PCT patent application gives extensive literature on studies with Melatonin and potential therapeutic application of various ligands reported till date.
Those various effects are exerted via the intermediary of specific Melatonin receptors. Molecular biology studies have demonstrated the existence of a number of receptor sub-types that are capable of binding that hormone (Trends Pharmacol. Sci., 1995, 16, p. 50; WO 97 04094). Melatonin acts on the CNS to affect neural mechanisms through receptors located in the brain. Additionally, a number of studies indicate the existence of direct effects of Melatonin in peripheral organs via peripheral melatonin receptors. Melatonin receptors are present in the heart, lungs, prostate gland; gonads, white blood cells, retina, pituitary, thyroid, kidney, gut and blood vessels (Withyachumnarnkul et al., Life Sci, 12 65, 1986). Three Melatonin receptor subtypes have been identified so far MT-I, MT-2 and Mel 1 c (Barreft et al., Biol. Signals Recept., 1999, 8: 6-14).
There is evidence suggesting both Melatonin agonists and antagonists would be of potential therapeutic use for a variety of maladies and conditions. PCT application WO 00/72815, discuss in depth applications and use of such compounds and details of which are incorporated herein by reference. Also U.S. Pat. No. 6,465,660 and U.S. patent application publication number US 2003/0105087 discuss some tricyclic indole and tricyclic azaindole derivatives having very valuable pharmacological characteristics in respect of melatoninergic receptors.
U.S. Pat. No. 4,839,377 and U.S. Pat. No. 4,855,314 refers to 5-substituted 3-aminoalkyl indoles. The compounds are said to be useful for the treatment of migraine.
British Patent 2,035,310 refers to 3-aminoalkyl-1H-indole-5-thioamides and carboxamides. The compounds are said to be useful in treating hypertension, Raymond's disease and migraine.
European Patent Publication 303,506 refers to 3-polyhydropyridyl-5-substituted-1H-indoles. The compounds are said to have 5-H1 receptor agonists and vasoconstrictor activity and to be useful in treating migraine. European Patent Publication 354,777 refers to N-piperidinylindolylethyl-alkane sulfonamide derivatives. The compounds are said to be 5-HT1 receptor agonists and have vasoconstrictor activity and are useful in treating cephalic pain.
European Patent Publication 438,230, refers to indole-substituted five-membered heteroaromatic compounds. The compounds are said to have “5-HT1-like” receptor agonist activity and to be useful in the treatment of migraine and other disorders for which a selective agonist of these receptors is indicated.
European Patent Publication 313,397 refers to 5-heterocyclic indole derivatives. The compounds are said to have exceptional properties for the treatment and prophylaxis of migraine, cluster headache and headache associated with vascular disorders. These compounds are also said to have exceptional “5-HT1-like” receptor agonism.
International Patent Publication WO 91/18897 refers to 5-heterocyclic indole derivatives. The compounds are said to have exceptional properties for the treatment and prophylaxis of migraine, cluster headache, and headache associated with vascular disorders. These compounds are also said to have exceptional “5-HT1-like” receptor agonism.
European Patent Publication 457,701 refers to aryloxy amine derivatives as having high affinity for 5-HT1D serotonin receptors. These compounds are said to be useful for treating diseases related to serotonin receptor dysfunction, for example, migraine.
European Patent Publication 497,512 A2, refers to a class of imidazole, triazole and tetrazole derivatives that are selective agonists for “5-HT1-like” receptors. These compounds are said to be useful for treating migraine and associated disorders.
International Patent Publication WO 93/00086 describes a series of tetrahydrocarbazole derivatives, as 5-HT1 receptor agonists, useful for the treatment of migraine and related conditions.
International Patent Publication WO 93/23396, refers to fused imidazole and triazole derivatives as 5-HT1 receptor agonists, for the treatment of migraine and other disorders.
Schoeffter P. et al. refers to methyl 4-{4-[4-(1,1,3-trioxo-2H-1,2-benzoisothiazol-2-yl)butyl]-1-piperazinyl}1H-indole-3-carboxylate as a selective antagonist for the 5-HT1A receptor in their paper “SDZ216-525, a selective and potent 5-HT1A receptor antagonist”, European Journal of Pharmacology, 244, 251-257 (1993).
International Patent Publication WO 94/06769, refers to 2-substituted-4-piperazine-benzothiophene derivatives that are serotonin 5-HT1A and 5-HT1D receptor agents useful in the treatment of anxiety, depression, migraine, stroke, angina and hypertension.